This disclosure relates to a medical device and more specifically to an implantable neuro stimulator that produces an electrical stimulation signal used to influence the human body.
The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions. Depending upon medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Clinicians use medical devices alone or in combination with drug therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. One type of medical device that can be used is an Implantable Neuro Stimulator (INS).
An INS generates an electrical stimulation signal that is used to influence the human nervous system or organs. Electrical contacts carried on the distal end of a lead are placed at the desired stimulation site such as the spine and the proximal end of the lead is connected to the INS. The INS is then surgically implanted into an individual such as into a subcutaneous pocket in the abdomen. The INS can be powered by an internal source such as a battery or by an external source such as a radio frequency transmitter. A clinician programs the INS with a therapy using a programmer. The therapy configures parameters of the stimulation signal for the specific patient's therapy. An INS can be used to treat conditions such as pain, incontinence, movement disorders such as epilepsy and Parkinson's disease, and sleep apnea. Additional therapies appear promising to treat a variety of physiological, psychological, and emotional conditions. As the number of INS therapies has expanded, greater demands have been placed on the INS. Examples of some INSs and related components are shown and described in a brochure titled Implantable Neuro stimulation Systems available from Medtronic, Inc., Minneapolis, Minn.
The effectiveness of the therapy as provided by the INS is dependent upon adjusting the electrical characteristics of the stimulation signal. For example, stimulation waveforms can be designed for selective electrical stimulation of the nervous system. Two types of selectivity may be considered. First, fiber diameter selectivity refers to the ability to activate one group of nerve fibers having a common diameter without activating nerve fibers having different diameters. Second, spatial selectivity refers to the ability to activate nerve fibers in a localized region without activating nerve fibers in neighboring regions.
The clinician may consider a number of factors such as the type of disorder and the specific condition of the patient in order to determine the electrical characteristics. The shape of stimulation waveform may be a factor in the effectiveness of the stimulation. Typically, a stimulation pulse may have a rectangular shape (“flat-topped”). However, a stimulation waveform with a slowly decaying trailing edge may prevent anodic break excitation. Also, a ramp-shaped stimulation waveform may generate selective activation of small nerve fibers. Thus, apparatus and method that provide a flexible and accurate capability of shaping a stimulation waveform is of importance in advancing the field of Implantable Neuro Stimulators.